Eddy current brake

ABSTRACT

An eddy current brake wherein a cupped rotor surrounds the coil and the pole shoes of the stator and is provided with inlets for admission of cool air when the coil is excited to produce in the rotor eddy currents with attendant generation of heat. The rotor has blades which serve to draw air into an internal rotor chamber and to circulate such air along the surfaces of the stator and rotor when the coil is excited. The inlets are controlled by a valve which is mounted in the stator and is movable between closed and open positions by actuating means which are also mounted in the stator. Such actuating means comprises electromagnets or temperature-responsive devices which employ heat-expandible elements.

United States Patent [72] lnventor Alfred Hoyler Stuttgart, Germany [211App]. No. 107,364 [22] Filed Jan. 18, 1971 [45] Patented Nov. 30, 1971 V73] Assignee Robert Bosch Gmbll Stuttgart, Gennany [54] EDDY CURRENTBRAKE 10 Claims, 4 Drawing Figs.

[52] U.S. Cl 310/93, 310/53, 310/94 [51] Int. Cl [102k 49/04 [50] Fieldof Search 3l0/92, 93, 94, 96, 53

[56] References Cited UNITED STATES PATENTS 2.440.55] 4/1948 Martin310/93 FOREIGN PATENTS 1,174,034 ll/l958 France Primary Examiner-D. X.Sliney AlrorneyMichael S. Striker ABSTRACT: An eddy current brakewherein a cupped rotor surrounds the coil and the pole shoes of thestator and is provided with inlets for admission of cool air when thecoil is excited to produce in the rotor eddy currents with attendantgeneration of heat. The rotor has blades which serve to draw air into aninternal rotor chamber and to circulate such air along the surfaces ofthe stator and rotor when the coil is excited. The inlets are controlledby a valve which is mounted in the stator and is movable between closedand open positions by actuating means which are also mounted in thestator. Such actuating means comprises electromagnets ortemperature-responsive devices which employ heat-expandible ele ments.

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INVENTOR. ALFRED HOYLER /a-zwxyw.

sum CURRENT BRAKE CROSS-REFERENCE TO RELATED APPLICATION Certainfeatures of the eddy current brake which is disclosed in thisapplication are claimed in my copending application Ser. No. l I 1,033filed Jan. 29, 1971 and entitled Aircooled eddy current brake.

BACKGROUND OF THE INVENTION The present invention relates toimprovements in eddy current brakes, especially to improvements in eddycurrent brakes for use in automotive vehicles. More particularly, theinvention relates to improvements in eddy current brakes of the typewherein a rotor surrounds and rotates with reference to the poles of anelectromagnet which is installed in the stator and wherein the rotor andthe stator are cooled when the brake is in use.

French Pat. No. 1,174,034 discloses an eddy current brake wherein heatwhich develops on conversion of braking energy is withdrawn by a coolantadmitted through an inlet controlled by a valve which is rotatably oraxially movably mounted on the hub of the rotor. The valve is actuatedby a magnetic ring which shares the movements of the rotor and isturnable with reference to the rotor by the magnetic filed whichdevelops on energization of the coil of the electromagnet on the stator,or by a bimetallic strip which is secured to the rotor and must beheated in order to undergo sufiicient deformation to actuate the valve.Since the rotor of an eddy current in an automotive vehicle is subjectto repeated acceleration or deceleration which is shared by the valve,the inertia of moving parts often causes the valve to assume positionswhich are not dictated by the need for a cooling action, i.e., the valveis likely to admit coolant or to prevent admission of coolant atinopportune times to thereby prevent proper cooling or to permit coolingat a time when the cooling action is not needed. The inertia of movingparts is likely to overcome the force of the magnet or to deform (bendor twist) the bimetallic element.

SUMMARY OF THE INVENTION An object of the invention is to provide aneddy current brake which is particularly suited for use in automotivevehicles and whose cooling system is constructed and mounted in such away that it is not affected by the inertia of moving parts or by otherforces which adversely influence the cooling action in conventional eddycurrent brakes.

Another object of the invention is to provide an eddy current brake withnovel means for actuating one or more valves which control the admissionof a fluid coolant into the range of coolant circulating means on therotor.

A further object of the invention is to provide an eddy current brakewherein the valve or valves which control the admission of coolant tothe cooling system need not be mounted on the rotor.

An additional object of the invention is to provide an eddy currentbrake with novel and improved means for actuating the valve or valveswhich control the admission of coolant into the range ofcoolant-circulating means on the rotor.

Still another object of the invention is to provide an eddy currentbrake wherein the cooling system and the means for actuating the valveor valves of the cooling system occupy little room and can operateindependently of all such factors which adversely affect the operationof cooling systems in presently known eddy current brakes.

The improved eddy current brake comprises a preferably annular statormember, a preferably cup-shaped rotor member which is preferably coaxialwith and rotates relative to the stator member with one or more partswhich must be braked at times determined by the operator of anautomotive vehicle, coil means mounted in or on the stator member andenergizable by the operator to produce in the rotor member eddy currentswith attendant generation of a braking force and heating of the twomembers, cooling means comprising coolant-admitting inlet means providedon the rotor member,

coolant-circulating means provided on and sharing angular movements ofthe rotor member to circulate along at least one of the two members acoolant which is admitted by way of the inlet means, and valve meanswhich is mounted on the stator member and is movable between open andclosed positions in which it respectively permits and prevents entry ofa coolant by way of the inlet means in the rotor so that such coolantcan flow into the range of the circulating means, and actuating meansprovided on the stator member and operative to move.

the valve means between the open and closed positions.

The actuating means may comprise one or more electromagnets and motiontransmitting linkages or the like which move the valve means to the openposition in response to energization or deenergization of theelectromagnets. It is also possible to employ one or moretemperature-responsive devices which cause the valve means to open inresponse to heating of one or more heat-expandible elements. Theelectromagnets are preferably energized or deenergized and theheat-expandible elements are preferably heated to move the valve meansto its open position in response to energization of the coil means onthe stator member, i.e., in response to generation of eddy currents. Thevalve means is preferably moved to its closed position with at leastsome delay following the deenergization of coil means to insure that thestator member and/or the rotor member is cooled for a fixed or variableinterval of time following the termination of a braking action.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved eddy current brake itself, however, both as to its constructionand its mode of operation, together with additional features andadvantages thereof, will be best understood upon perusal of thefollowing detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial sectional view of aneddy current brake which embodies one form of the invention and whereinthe actuating means for the valve means comprises several electromagnetswhich must be deenergized in order to move the valve means to its openposition;

FIG. 2 is a fragmentary axial sectional view of a second eddy currentbrake wherein the electromagnets of the actuating means must beenergized in order to move the valve means to its open position;

FIG. 3 is a diagram of the electric circuit of the eddy current brake ofFIG. 2; and

FIG. 4 is a fragmentary axial sectional view of a third eddy currentbrake wherein the actuating means comprises one or more heat-responsivedevices which must be heated in order to move the valve means to itsopen position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS stator. The central opening ofthe stator II contains an an-- tifriction bearing 15 which is surroundedby a hub or sleeve I6 rotatable with a stub shaft 17 which constitutesthat rotary part of the transmission or differential which is to bebraked when the coil 12 is energized.

The hub 16 has a radially outwardly extending flange 18 which is securedto a drum-shaped rotor 20 by fastener means 180. The rotor 20 includes acylindrical portion 21 which surrounds, with some clearance, the outerfaces of the claws of pole shoes 13 and 14. Such outer faces form partof a cylindrical surface. When the coil 12 is excited, it produces amagnetic field which acts on the cylindrical portion 21 of the rotorthrough the pole shoes 13, 14 and tends to arrest the rotor whereby thelatter brakes the shaft 17 through the intermediary of the hub 16.Excitation of the coil 12 results in generation of eddy currents in therotor 20 and the energy of such eddy currents is converted into heatwhich is dissipated in accordance with a feature of the presentinvention.

The rotor 20 further comprises an annular bottom wall or end wall 22whose central portion is affixed to the flange 18 of the hub 16 by thefastener means and which is provided with several air-admitting inletsor openings 23 adjacent to the flange 18. The inlets 23 are separatedfrom each other by spokes or partitions 24 of the end wall 22. The endwall 22 is further provided with a ring-shaped chamber 25 which cancommunicate with the atmosphere by way of the inlets 23 and whichfurther communicates with radially outwardly extending passages orchannels 26 of the end wall 22. The channels 26 are separated from eachother by air-circulating vanes or blades 27 whose aerodynamic design issuch that, when the rotor 20 is driven by the shaft 17, the vanes 27draw air into the chamber 25 by way of the inlets 23 and the vanes 27thereupon push the thus drawn air from the chamber 25 into the channels26 and along cooling ribs or fins 28 which extend substantially axiallyof the shaft 17 and are machined into the external surface of thecylindrical portion 21. The fins 28 define axially parallel flutes orgrooves wherein the air flows in a direction to the right, as viewed inthe drawing. The fins 28 are surrounded by a cupped shroud 29 whichseparates the flutes 30 from each other and overlies the outer portionof the end wall 22. The shroud 29 can be made of sheet metal.

The inner side of the end wall 22 is formed with radial aircirculatingblades or vanes 33 which extend toward the adjacent end face of thestator 11 and serve to draw some air from the chamber 25 when the rotor20 is driven by the shaft 17 and the inlets 23 are free to admit coolatmospheric air. Such air then flows through the gaps between the clawsof the pole shoes 13, 14 to issue at the right-hand axial end of thestator 11, as viewed in the drawing The chamber 25 accommodates aslightly conical ringshaped axially reciprocable valve 35 which can bemoved from the open position shown by solid lines to a closed or sealingposition 35' (shown by phantom lines) in which it seals the inlets 23 toprevent admission of air into the chamber 25. The left-hand end surfaceof the valve 35 is dimensioned in such a way that the valve practicallyseals the chamber 25 from the inlets 23 when it assumes the phantom-lineposition 35'.

The actuating means for moving the valve 35 between the open and closedpositions comprises a linkage including three equidistant axiallyreciprocable motion transmitting rods 36 which are parallel to the shaft17 and are reciprocable in axially parallel bores 37 of the stator 11,and three additional motion transmitting elements 38 each of whichconstitutes a twoarmed lever. The levers 38 are fulcrumed on bearingblocks 39 which are provided on the stator 11 and their longer arms arearticulately connected with the exposed ends of the adjacent rods 36.The shorter arms of the levers 38 are articulately connected toreciprocable armatures 40 of three equidistant valve-displacingelectromagnets 42 which are installed in recesses or blind bores 41 ofthe stator 11. The axes of the rods 36 are located on the periphery ofan imaginary cylinder which is coaxial with the shaft 17 and with thecylindrical portion 21 of the rotor 20.

The bores 37 for the rods 36 have enlarged outer end portions 43 whichreceive helical springs 45 each of which bears against the longer arm ofthe respective lever 38 and tends to maintain the rod 36 in theillustrated position corresponding to the open (solid-line) position ofthe valve 35. When the electromagnets 42 are energized, the armatures 40move in a direction to the right, as viewed in FIG. 1, whereby thelevers 38 pivot against the opposition of the respective springs 45 andcause the rods 36 to move the valve 35 to the closed or sealing position35 It will be seen that, when the electromagnets 42 are deenergized, thevalve 35 dwells in the open position in which the inlets 23 can admitair into the chamber 25 of the end wall 22. The arrangement is normallysuch that, when the electromagnets 42 are energized. the valve 35 ismoved to a closed position in which it is closely adjacent to the inlets23 so that it nearly completely seals the chamber 25 from theatmosphere. The vanes 27 and the blades 33 are then unable torespectively draw air from the atmosphere and from the chamber 25. Thesevanes and blades become effective as soon as the electromagnets 42 aredeenergized so that the springs 45 are free to expand and to return thevalve 35 to the solid-line position. The air which is drawn by the vanes27 into the chamber 25 and is thereupon pushed into the channels 26 andflutes 30 serves to cool the fins 28 and hence the cylindrical portion21 of the rotor 20. The streams of air which are drawn from the chamber25 by the blades 33 cool the outer sides of the pole shoes 13, 14, theouter side of the coil 12 and the internal surface of the cylindricalportion 21.

The circuit of the electromagnets 42 is designed in such a way that theelectromagnets 42 are deenergized in response to energization of thecoil 12. This insures that the blades 33 and vanes 27 are capable ofcooling the aforedescribed parts of the brakes when the control systemfor the electromagnets 42 becomes inoperative or when the source whichfurnishes electrical energy for energization of the electromagnets 42 isexhausted. Thus, the parts of the brake are invariably cooled when thecoil 12 is energized, irrespective of whether the control system for theelectromagnets 42 is operative or not because, when the control systemis out of commission, the electromagnets 42 are deenergized and thesprings 45 are free to maintain the valve 35 in the open position.

In accordance with another feature of the invention, the energization ofelectromagnets 42 continues for a certain interval following the openingof the circuit of the coil 12. This insures that the vanes 27 and blades33 can effect complete or substantially complete cooling of the stator11 and rotor 20 upon termination of the braking action. To this end, thepole face of one of the pole shoes 13, 14 (for example of the pole shoe14) is provided with a detector here shown as an NTC-resistor 51 whoseelectrical resistance varies as a function of its temperature and whichis in circuit with the electromagnets 42 by way of a suitable signalamplifier (not shown in FIG. 1) to insure that the electromagnets 42 areenergized with a certain delay following deenergization of the coil 12.Thus, the electromagnets 42 are energizable upon deenergization of thecoil 12 but with such a delay that the valve 35 returns to thephantom-line position 35' only after the cooling of the stator 11 androtor 20 to a desired temperature is completed. As mentioned above,energization of the coil 12 takes place simultaneously withdeenergization of the electromagnets'42 to insure that the stator androtor of the brake are cooled during the application of a brakingaction, i.e., when the magnetic field induced by the excited coil 12produces eddy currents in the rotor 20.

An important advantages of the improved eddy current brake is that thevalve 35 is mounted on the stator 11 so that its positions can bedetermined by actuating means which is also installed in or on thestator. Therefore, the positions of the valve 35 can be determinedindependently of inertia of rotating parts or other factors whichinfluence the position of a valve on the rotor. Another advantage ofsuch mounting of the valve 35 and of the actuating means therefor isthat particles of dirt or other foreign matter which deposit on therotor are less likely to interfere with movements of the valve betweenits open and closed positions.

The improved brake is susceptible of many modifications withoutdeparting from the spirit of the invention. For example, the armaturesof the electromagnets 42 can be designed to pull, rather than push, theadjacent arms of the levers 38 when the valve 35 is to move toward itsclosed position.

This is shown in FIG. 2 wherein all such parts which are clearlyanalogous to or identical with the corresponding parts of the eddycurrent brake shown in FIG. 1 are denoted by similar referencecharacters. The springs 45 react against a retaining ring 46 for thebearing in the stator 11 and bear against washers 40b on the respectivearmatures 40 so that they normally urge the armatures in a direction tothe left, as viewed in H6. 2. The levers 38 then cause the rods 36 tomove the valve 35 to the closed position which is indicated by phantomlines. The electromagnets 42 are energizable simultaneously with thecoil 12 by a control circuit which is shown in FIG. 3. This controlcircuit includes a starter switch 50 which is closed by the operator ofthe vehicle when the brake is to apply a braking force to the shaft 17.The electromagnets 42 are energized and cause the linkage including therods 36 and levers 38 to move the valve 35 to the open position. Thetime delay means for delaying the deenergization of electromagnets 42and hence the closing of the valve 35 under the action of the springs 45comprises a detector 51 which is mounted on one of the pole shoes 14 andmeasures the temperature of the adjacent parts. When such temperaturereaches a predetermined value which indicates that the stator 11 and therotor are sufficiently cooled by air which is circulated by the vanes27, the detector 51 produces a signal which is amplified by an amplifier52 whereby the latter opens the circuit of the electromagnets 42. Thepositive pole of the energy source which is connectable by starterswitch 50 with the electromagnets 42 and coil 12 is indicated at 500. Afirst diode 53 is installed in the conductor between the starter switch50 and electromagnets 42 to prevent the pulse generated by the amplifier52 from reaching the coil 12. A second diode 54 prevents the currentwhich flows to the windings of the electromagnets 42 when the switch 50is closed from influencing the amplifier 52. The numeral 55 denotes asignal lamp which is preferably mounted on the dashboard of the vehicleand can be observed by the driver so that the driver is notified thatthe valve 35 is held in the open position. If desired, the lamp 55 canbe caused to light up only when the parts 11, 20 are heated to anelevated temperature which warrants temporary stoppage of the vehicleafter a prolonged application of the brake, for example, while thevehicle travels along an elongated downwardly sloping portion of amountain road.

The detector 51 can constitute an NTC-resistor whose resistance variesin response to heating or cooling.

It is further possible to replace the valve actuating means of F l0. 1or 2 with an actuating means which comprises one or moretemperature-responsive valve displacing devices 55 one of which is shownin FIG. 4. The valve 35 can be moved to its open position in response toheating of a heat-expandible element 61 which is mounted in the stator11 in the interior of a casing 56 forming part ofthe device 55. Adiaphragm 57 which is at least partially surrounded by the element 61 isconnected with a piston 58 which is articulately connected to the medianportion of a motion transmitting lever 60. The latter is pivotable withreference to a bearing block 39 and has a bifurcated end portionstraddling a pin on a motion transmitting rod 36 coupled to the valve35. The casing 56 is strongly resistant to deformation and is surroundedby a heating member 59 here shown as a coil of electric resistance wirewhich is connected with an energy source by the starter switch 50 (notshown in FIG. 4) when the latter completes the circuit of the coil 12.The heat generated by wire 59 then preferably melts the element 61 whichexpands and pushes the diaphragm 57 in a direction to the right to openthe valve 35. The vanes 27 then circulate the coolant which is admittedby way of the inlets 23. That portion of the stator 11 which surroundsthe wire 59 and casing 56 serves as a time delay means which insuresthat the material of the elements 61 sets and contracts with at leastsome delay following opening of the circuit of the coil 12 and wire 59.This insures that the parts 11, 20 are cooled after the coil 12 isdeenergized, preferably for an interval of time which is sufficient toinsure that the temperature of the parts 11, 20 drops below a certainvalue. The diaphragm 57 automatically returns the valve 35 to its closedposition when the temperature of the casing 56 drops sufficiently topermit a substantial contraction of the element 61. It is clear that thedevice 55 can be replaced by one or more temperature-responsive deviceswhich are capable of directly engaging and displacing the valve 35 orone or more valves which perform the functions of the valve 35.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of my contribution to the art and, therefore, suchadaptions should and are intended to be comprehended within the meaningand range of equivalence of the claims.

What is claimed as new and desired to be protected by U.S. Patent is setforth in the appended What is claimed:

1. In an eddy current brake, particularly for use in automotivevehicles, a combination comprising a stator member; a rotor memberrotatable with reference to said stator member; coil means mounted insaid stator member and energizable to produce in said rotor member eddycurrents with attendant application of a braking force and heating ofsaid members; cooling means comprising coolant-admitting inlet meansprovided on said rotor member, coolant-circulating means provided onsaid rotor member to circulate along at least one of said members acoolant which is admitted by way of said inlet means, and valve meansprovided on said stator member and movable between open and closedpositions in which it respectively permits and prevents entry of coolantinto the range of said circulating means by way of said inlet means; andactuating means provided on said stator member and operable to move saidvalve means between said open and closed positions.

2. A combination as defined in claim 1, wherein said valve means ismovable axially of said rotor member.

3. A combination as defined in claim 2, wherein said actuating meanscomprises displacing means and a motion transmitting linkage connectingsaid displacing means with said valve means.

4. A combination as defined in claim 3, wherein said displacing meanscomprises at least one electromagnet.

5. A combination as defined in claim 1, wherein said actuating meanscomprises at least one electromagnet and further comprising controlmeans for energizing said electromagnet, said control means comprisingtemperature responsive detector means arranged to measure thetemperature of at least one of said members and to produce a signal inresponse to detection of a predetermined temperature, and amplifiermeans for energizing said electromagnet in response to said signal.

6. A combination as defined in claim 1, wherein said actuating meanscomprises electromagnet means and motion transmitting means for movingsaid valve means to said closed position in response to energization ofsaid electromagnet means.

7. A combination as defined in claim 1, wherein said actuating meanscomprises at least one electromagnet and motion transmitting means formoving said valve means to said closed position in response todeenergization of said electromagnet.

8. A combination as defined in claim 1, wherein said actuating meanscomprises at least one temperature-responsive device and motiontransmitting means for moving said valve means to said open position inresponse to heating of said device. 1

9. A combination as defined in claim 8, wherein said device comprises aheat-expansible element and heating means for heating said element inresponse to energization of said coil means.

10. A combination as defined in claim 1, wherein said stator member is aring-shaped member and said rotor member is coaxial with and surroundsat least a portion of said stator member, said rotor member having anend wall and said inlet means being provided in said end wall, said endwall further having a chamber communicating with said inlet means in theopen position of said valve means and said circulating means beingarranged to draw a coolant into said chamber in the open position ofsaid valve means and to expel the thus drawn coolant from said chamberalong a plurality of paths wherein the coolant exchanges heat with atleast one of said members.

i I! l i l

1. In an eddy current brake, particularly for use in automotivevehicles, a combination comprising a stator member; a rotor memberrotatable with reference to said stator member; coil means mounted insaid stator member and energizable to produce in said rotor member eddycurrents with attendant application of a braking force and heating ofsaid members; cooling means comprising coolant-admitting inlet meansprovided on said rotor member, coolant-circulating means provided onsaid rotor member to circulate along at least one of said members acoolant which is admitted by way of said inlet means, and valve meansprovided on said stator member and movable between open and closedpositions in which it respectively permits and prevents entry of coolantinto the range of said circulating means by way of said inlet means; andactuating means provided on said stator member and operable to move saidvalve means between said open and closed positions.
 2. A combination asdefined in claim 1, wherein said valve means is moVable axially of saidrotor member.
 3. A combination as defined in claim 2, wherein saidactuating means comprises displacing means and a motion transmittinglinkage connecting said displacing means with said valve means.
 4. Acombination as defined in claim 3, wherein said displacing meanscomprises at least one electromagnet.
 5. A combination as defined inclaim 1, wherein said actuating means comprises at least oneelectromagnet and further comprising control means for energizing saidelectromagnet, said control means comprising temperature responsivedetector means arranged to measure the temperature of at least one ofsaid members and to produce a signal in response to detection of apredetermined temperature, and amplifier means for energizing saidelectromagnet in response to said signal.
 6. A combination as defined inclaim 1, wherein said actuating means comprises electromagnet means andmotion transmitting means for moving said valve means to said closedposition in response to energization of said electromagnet means.
 7. Acombination as defined in claim 1, wherein said actuating meanscomprises at least one electromagnet and motion transmitting means formoving said valve means to said closed position in response todeenergization of said electromagnet.
 8. A combination as defined inclaim 1, wherein said actuating means comprises at least onetemperature-responsive device and motion transmitting means for movingsaid valve means to said open position in response to heating of saiddevice.
 9. A combination as defined in claim 8, wherein said devicecomprises a heat-expansible element and heating means for heating saidelement in response to energization of said coil means.
 10. Acombination as defined in claim 1, wherein said stator member is aring-shaped member and said rotor member is coaxial with and surroundsat least a portion of said stator member, said rotor member having anend wall and said inlet means being provided in said end wall, said endwall further having a chamber communicating with said inlet means in theopen position of said valve means and said circulating means beingarranged to draw a coolant into said chamber in the open position ofsaid valve means and to expel the thus drawn coolant from said chamberalong a plurality of paths wherein the coolant exchanges heat with atleast one of said members.